In recent years and continuing, optical disks (e.g., CDs (Compact Disc) and DVDs (Digital Versatile Disc)) serving to record computer programs, audio information, video information (hereinafter referred to as “contents”) are drawing greater attention owing to the advances in digital technology and the improvements in data compression technology. Accordingly, as the optical disks become more inexpensive, optical disk apparatuses for reproducing the information recorded in the optical disks have grown to become widely used.
CD type optical disks that are available in the market include, for example, CD-R (CD-Recordable) and CD-RW (CD-Rewritable). DVD type optical disks that are available in the market include, for example, DVD-RAM, DVD-R (DVD-Recordable), DVD-RW (DVD-Rewritable), and DVD+RW (DVD+Rewritable).
The amount of information to be recorded in the optical disks is growing year by year. Therefore, further increase in the recording capacity of a single optical disk is expected. As for measures that are being developed for increasing the recording capacity of the optical disk, there are, for example, (1) increasing recording density and (2) increasing recording layers (see, for example, Japanese Laid-Open Patent Application No. 2001-126255 showing a method of recording information in a rewritable information recording medium having plural recording layers).
Drive apparatuses and optical disk players which are dedicated to reproducing read-only optical disks (e.g. CD-ROMs and DVD-ROMs) (hereinafter referred to as “reproduction only drive apparatuses”) are already widely used. It is desired that these reproduction-only drive apparatuses also be able to reproduce recordable optical disks including rewritable type optical disks (e.g. CD-RW, DVD-RW, DVD+RW, DVD-RAM) and recordable type optical disks (e.g. CD-R, DVD-R).
Meanwhile, it is desired that rewritable optical disks, in particular, be able to perform random access for rewriting part of their data.
However, in some cases, being able to be reproduced by a reproduction only drive apparatus and being able to perform random access are difficult to achieve at the same time. For example, in a random access recorded optical disk, the optical disk includes recorded areas and unrecorded areas provided thereon in a scattered manner. Accordingly, in a case where such an optical disk is set in a reproduction only drive apparatus, reproduction error (e.g. uncontrollability and/or address error due to inability to obtain a proper address) may occur when a light beam is condensed onto an unrecorded area of the optical disk.